Protein complexes assembly, structure and function

Abstract:  Most proteins must fold into their native conformations to fulfil their biological functions. Failure of proteins to fold leads to cell pathology and a broad range of human diseases referred to as protein misfolding disease, e.g., Alzheimer’s disease, Parkinson’s disease, and type II diabetes. More than 40 proteins are known to be connected with misfolding diseases. These proteins share no sequence homology but all assemble into cross-b sheet containing insoluble fibrillar aggregates. Despite the pathological conditions that these proteins can induce, living organisms can take advantage of the inherent ability of these proteins to form such structures and to generate novel and diverse biological function, the functional amyloid. This thesis examines different aspects of cross-b sheet containing aggregates. The first paper describes the humoral response to aggregated structures of insulin and the astrocytical biomarker S100B in patients suffering from Parkinson’s disease. We show that the patients have an increased immunreactivity towards insulin and S100B in Parkinson’s disease patients compared to a control group. The second part of this work focuses on a functional amyloid. HAMLET (human a-lactalbumin made lethal for tumour cells) is a complex of a-lactalbumin and oleic acid, which kills tumour cells but not healthy differentiated cells. We wish to expand the concept of HAMLET to a structurally related protein and therefore create and characterize a complex of equine lysozyme and oleic acid (Paper II). We chose equine lysozyme because both proteins (equine lysozyme and a-lactalbumin) share common ancestors and are spatially related. The newly designed complex was named ELOA, for equine lysozyme with oleic acid. ELOA represents a functional oligomer due to its multimeric state and its ability to bind amyloid specific dyes. In the third paper, we investigate the interaction of the cytotoxic ELOA with live cells in real time to find a mechanistic model (Paper III). It is known that HAMLET is not only tumouricidal but is also toxic towards many bacteria. Therefore in the last part of the thesis, we investigated the effects of ELOA on different bacterial strains and focused on its interplay Streptococcus pneumoniae (Paper IV). These studies have added significantly to many aspects of protein folding and misfolding from its involvement in Parkinson’s disease to the newly gained functions and structural aspects of de novo produced ELOA.